1. Field of the Invention:
The present invention relates to an electric machine apparatus such as a solid state commutator motor wherein the current is fed to AC windings by an inverter or a power converter using solid state switches.
2. Description of Prior Art:
The combinations of the solid state AC feeder with various AC motors such as a non-commutator motor, a thyristor motor and an inverter type induction motor have been known. These motors are solid state commutating motors using solid state switches as a commutator.
The combinations of the current type converter with the synchronous motor or the induction motor have been well-known as a non-commutator motor and a current type variable frequency inverter because the motor driving and the regenerative braking operation can be economically attained.
FIGS. 1(a), (b) are connection diagrams of the conventional inverter type solid state commutator motors. In FIG. 1, the references p and N designate DC input terminals; (4) designates a smoothing reactor; (300) designates a solid state commutator connected in bridges (inverter); (100) designates AC windings of the AC motor.
The AC windings of the conventional AC motor are connected in three or six phases, whereby the solid commutator (300) comprises solid switches connected in three phase bridges or six phase bridges.
The combination of the three phase AC windings and the three phase bridges shown in FIG. 1(a) has been widely used. However, the AC windings of the three phase AC motor have the inner connection shown in FIG. 1(c) wherein pairs of windings in the relation of reverse phase (U, U) (V, V) (W, W) are respectively connected in series, whereby it has the six phase structure in inner structure though it seems to be three phase structure.
The sectional space distributing region of the winding conductors can be shown in FIG. 1(d), wherein the conductor distributing region for one phase (phase belt) is the electric angle of .pi./3 and the six groups of coils U, V, W, U, V, W, are disposed. The return conductor distributing regions of the groups of coils are shown as U', V', W', U', V', W'. The coils pitches of the coils are usually short pitches. In the short pitches, the return conductors are disposed in the positions shifting for the electric angle .pi..
As it is clearly understood, the three phase connection in FIG. 1(a) has the six phase winding structure in fact, whereby the winding operation required for the six phase connection of FIG. 1(b) is needed.
On the solid state commutator, in the embodiment of FIG. 1(a), commutation is performed 6 times in one cycle. In FIG. 1(b), one of the positive solid state switches (3aP) to (3fP) and one of the negative solid state switches (3aN) to (3fN) are turned on and off in one phase. For example, the switches (3aP) and (3dN) are simultaneously controlled to turn on and off.
On the AC windings, the windings U and U, V and V or W and W are simultaneously commutated. Accordingly, in the six phase connection of FIG. 1(b), the commutations are performed 6 times in one cycle.
The characteristics and the winding structure of the motor are the same for both of the connections of FIGS. 1(a) and (b). The connection of FIG. 1(b) has no merit on the two times of the phases.
In the solid state commutator motor, the torque pulsations are caused 6 times in one cycle and the torque pulsation is disadvantageously large. When it is commutated by the inner electromotive force of the AC windings of the motor, or the cage type induction motor is driven, the AC winding power-factor is inferior and the torque pulsation is remarkably large, disadvantageously.